Microcomputers and other computers frequently use a magnetic data storage disk enclosed in a casing which can be inserted and withdrawn from a disk drive to enter data into the computer or transfer data from one computer to another. Currently, a very popular form of these disks is the 31/2 inch diskette. These diskettes have a round magnetic data storage disk within a brittle plastic casing. The casing has a top layer and a lower layer and is sealed around the edges in order to protect the disk from the outside environment. A sliding metal sleeve covers a portion of the disk and is pulled back by the disk drive in order to read data to and from the disk. These disks are sold in two formats, double density and high density. A high density disk stores twice the data that a double density disk does. Normally, either type of disk can be inserted into the same disk drive. The casings for the two disks are identical except for a hole molded into the high density disk casing which is not present in the double density disk casing. The disk drive detects the presence of this molded-in hole and formats the data differently when the hole is present.
In order to minimize production costs, the only differences between most high density 31/2 inch diskettes and most double density 31/2 inch diskettes are the quality control which they must pass and the casing in which they are mounted. In order to save production costs, high density and double density disks are usually produced in exactly the same way on the same production line. However, high density disks, having passed a more stringent quality control test, typically cost two or three times as much as double density disks.
As a result, it would be desirable to alter the casing of a double density disk so that the disk drive would treat the disk as a high density disk. Since the disks are essentially identical except for the casing, and twice as much data can be stored on a high density disk, the cost of and number of disks needed for any particular task could be significantly reduced. Unfortunately, it is quite difficult to alter the molded casings. The disk casings are typically made from a virtually rigid, brittle plastic material which is difficult to cut without cracking, bending or deforming the casing material. If the casing is cracked or bent, data cannot be read properly. If small casing particles, produced when the disk is cut, contact the magnetic storage disk within the casing, then the disk is destroyed. In addition, to maintain the integrity of the casing, it is best if the casing edge is not cut but instead a hole is cut in the disk spaced apart from the disk's edge.